Boosters for relatively insensitive high ammonium nitrate explosives



3,341,382 BOOSTERS FOR RELATIVELY INSENSITIVE HIGH AMMONIUM NITRATE EXPLOSIVES Melvin A. Cook, Salt Lake City, Utah, and Henry E. Farnam, .lr., Saguenay, Quebec, Canada, assignors to Iron Ore Company of Canada, Wilmington, DeL, a corporation of Canada No Drawing. Filed Apr; 28, 1964, Ser. No. 363,290 7 Claims. (Cl. 149-15) This invention relates to the combination of high ammonium nitrate explosives and the booster for such explosives. The present application is a continuation-in-part of application Ser. No. 766,698, filed Oct. 13, 1958, which was a continuation-in-part of application Ser. No. 701,330, filed Dec. 9, 1957, both now abandoned.

One of the types of explosives with which boosters are combined in accordance with this invention are the prilled ammonium nitrate and fuel oil mixtures currently in large scale use in large diameter well-drill blasting, for example, in iron ore mining, quarrying and the like. It has previously been the practice to provide loose fine grained TNT or dynamite as a booster for this explosive. Such previously used boosters have the disadvantage that a large quantity of the booster is necessary to insure reliable detonation. Reliable detonation means substantially complete explosion with propagation throughout the full length of a long slender column, e.g., in a column at least five or six times as long as its diameter.

In the combination in accordance with our invention a high ammonium nitrate explosive is combined with a booster having a detonation pressure in excess of 130 kilo atmospheres. We have found, as will be exemplified in the detailed examples given herein, that the booster provided in accordance with this invention can be as little as /3 the size of the previously used loose fine grained TNT booster. The detonation pressure p is described by the hydrodynamic theory of detonation as the pressure at the Chapman-Jouguet plane and has been found in accordance with this invention to be of great importance in determining the effectiveness of a booser for detonating high ammonium nitrate explosives. Thus, while one may achieve detonation, for example, in AN (prilled)-fuel oil ranging in compositions from 99 to 90 percent AN and 1 to 10 percent fuel oil with a large enough quantity of a low pressure explosive, such as loose, fine grained TNT or dynamite of p =50 to 80 kiloatm., detonation with reliable propagation, particularly in a long column, i.e., in excess of five or six times its length, may be achieved consistently and assuredly with a much smaller amount of the very high pressure explosives such as cast or pressed 50/50 pentolite (P =210 kiloatm.), pressed tetryl (130 P l60 kiloatm.), pressed RDX or RDX- Wax and similar high pressure types included in this invention.

Other examples of relatively insensitive explosives which may elfectively and economically he detonated by boosters of the type contemplated by this invention are the ammonium nitrate (AN)-trinitrotoluene-water, ammonium nitrate-aluminum-trinitrotoluene-water and aluminum- Water and ammonium nitrate mixtures described in our copending Canadian applications 740,642 filed Nov. 21, 1957, and 746,481 filed Feb. 28, 1958. These correspond respectively to US. applications by the present inventors, Ser. No. 701,330, filed Dec. 9, 1957, now abandoned,

3,341,382 Patented Sept. E2, 1967 and Ser. No. 766,729, later issued as US. latent No. 3,121,036, on Feb. 11, 1964, and reissued as No. 25,695,

Dec. 8, 1964. Our invention provides a particular and unexpected advantage in conjunction with these water compatible explosives as the combination provides an explosive which can be detonated in the presence of water. This is of great value as it is often almost impossible or very costly to exclude water during mining and quarrying. The explosive composition and the boosters contemplated in accordance with this invention can be used in the presence of water for different reasons. In the case of the explosive composition the water enters into the explosive reaction, as described in the copending applications referred to above, whereas the boosters selected in accordance with this invention can be used in the presence of water by virtue of their water resistance. Furthermore, in the case of water slurry compositions, the continuous aqueous medium assists in generation and propagation of the detonation wave energy, as explained more fully in the copending applications mentioned above. Thus in the case of water compatible explosives there is an important combination between a water compatible explosive and a water resistant booster.

Other ammonium nitrate containing compositions with which boosters of the type contemplated by this invention can be used include loose, granular mixtures of ammonium nitrate-carbon black; ANDNT; AN-Z-nitropropane and similar mixtures especially when formulated with coarse, guhr coated AN (e.g., prilled AN).

The class of booster that can be used in accordance with this invention may be defined as follows: The first requirement is that the detonation pressure he in excess of kilo atmospheres for the reasons previously indicated. Another property that should be possessed by the booster is that it must itself be capable of being readily detonated, for example, by attachment to a trunkline of pentaerythritol tetranitrate core fuse, sold under the trademark Primacord detonating fuse of standard and well known type, or equivalent primary detonator. Therefore, a high detonation pressure explosive of a sensitive type must be employed. The booster must also be safe, that is to say, it must be capable of being handled safely under normal conditions and using reasonable precautions. Hence it should not be unduly sensitive. The booster should have the necessary mechanical strength to avoid breakup under normal use, using reasonable care. Water resistance is important and is indeed essential in the case of explosives which are to be used in the presence of water so that the explosive can be detonated under Water as well as in dry holes.

We have found that cast pentolite having TNT and PETN in the ratio of 50/50 provides all the requisite properties for an ideal booster for ammonium nitrate explosives; however, in accordance with this invention in its broadest aspects the booster may be selected from the following materials, namely, pressed tetryl, pressed tetryl containing up to 2% graphite preferably packaged in a paper or plastic shell to provide the necessary mechanical strength. Other examples are pressed RDX (cyclotrimethylenetrinitramine), or pressed waxed RDX, and cast or pressed pentolite.

We have discovered that mixtures of AN-coarse TNT- water described in the companion applications referred to above and having 15 to 20 percent water (or the amount required for slurrying the mixture) may be deto- '5 3 nated satisfactorily and reliably in say diameter charges more or less, at AN/TNT ratios from zero to five, with cast 50/50 pentolite boosters ranging from 1 diameter g. to 2 diameter-160 g. depending on the AN/ TNT ratio. In any particular case where comparisons were made more pressed tetryl was required to cause detonation than with cast 50/ 50 pentolite.

We have discovered that the minimum booster sensitiveness of these insensitive types of high ammonium nitrate explosives may, for any given booster, be related roughly to the critical diameter of the explosive, For example, when the critical (unconfined) diameter is 4 one generally requires between and 80 g. of pressed tetryl 'or between 20 and 60 g. of cast 50 pentolite to detonate the mixture. With loose, fine grained TNT boosters, or with average dynamite boosters (e.g., 40 to 50 percent dynamites) an explosive having a 4" critical diameter usually requires 500 g. or more booster to detonate it in diameters at or above the critical diameter. On the other hand, if its critical diameter is about 9", the explosive can usually be detonated with about a 2 (d.)-460 to 300 g. pressed tetryl booster, but an explosive with a 9" critical diameter in general requires much larger, loose, fine TNT, dynamite, or similar low density boosters to detonate it. Since one requires some margin of safety in both diameter (above the critical one) and in booster size (above the minimum booster) it is usually not practical to use, for example, in 9" boreholes an explosive having a critical diameter greater than say about 5" and a minimum booster greater than about 2"50 to 75 g. cast 50/50 pentolite. Moreover, to detonate such explosives with an adequate margin of safety one requires the use of a booster at least twice as large as the minimum booster required to obtain consistent detonations under controlled laboratory conditions.

Laboratory conditions ordinarily are designed to test columns about six times as long as their diameter. Failure of any significant part of the column to explode is considered a detonation failure. Therefore, a 2" (d.)160 g. 50/50 pentolite booster should normally provide all the boostering action required of any insensitive type explosive that is practical for use in large diameter blasting of the type described above. In many operations, moreover, it may be practical to use say 1.5 (d.)-80 to 100 g. cast pentolite boosters or comparable RDX or tetryl, or other high pressure boosters, and still have enough margin of safety or assurance of performance for practical application. To provide the same boostering action with dynamite or, as in Nitramon primers with fine grained, loose packed TNT, amatol, or sodamatol, one requires at least eight times and possibly considerably more explosive than with the preferred cast or pressed pentolite or tetrylboosters described in this invention.

The nature of manner of carrying out our invention will be further apparent from the following examples:

Example 1 In one series of measurements the minimum boosters required to detonate a 94.5/ 5.5 prilled AN-No. 2 fuel oil mixture packed at a density of 0.8:003 g./cc. were determined, using 9" diameter (d.) X 50" or more long (L) charges to be as follows:

Booster: Minimum booster charge required Cast 50/50 pentolite Less than 1" (d.)-40

grams. Pressed tetryl (l percent graphite 1" (d.)-40 grams. Loose, fine grained TNT (density 0.8 g./cc.) 3" (d.)-300 grams.

This example shows that only as much tetryl and less than /8 as much 50/50 pentolite are required to detonate 4. a 94.5/ 5.5 AN-fuel oil mixture than the amount required to achieve detonation of those charges using loose, fine grained TNT.

Example 2 A 94.5/5.5 AN (prill)-No. 2 fuel oil composition at density 0.8-$0.03 g./cc. was found to have a 4" critical diameter for unconfined charges greater than 50 long. However, it was found to propagate using the high pressure boosters in lengths of between 25 and 40" in 3"- diameter charges. Using 3" (d.) x 25" (L) charges the following booster sensitivity results were obtained:

Booster: I Results Pressed tetryl (1 percent graphite) 2" (d.)-200 g.: 4D, 0F.* Do 2" (d.)-g: 1D. Do 1" (d.)-60 g.: 1D, 3F. Nitramon S (2- pound can) 5F.

*Dzdetonated complete length; Fzfailed to detonate 3 x 25" charge.

What is claimed is:

1. In combination, a mass of high ammonium nitrate explosive containing a major proportion of said nitrate and a fuel oil, said mass being insensitive to reliable detonation by ordinary pentaerythritol tetranitrate core fuse, and having in a long column a critical diameter of at least 4 inches, and a sensitive booster capable of producing a detonation pressure of at least kilo atmospheres and composed primarily of water resistant material selected from the group which consists of pressed and cast pentolite, pressed tetryl and pressed cyclotrimethylenetrinitramine, said booster having a mass of at least 20 grams to assure reliable detonation of said mass of high explosive.

2. The method of blasting with a liquid-plasticized high ammonium nitrate composition containing water and 3.111- minum and which has a density of at least about 0.8 gram per cublic centimeter and has in a long column a critical diameter of at least about 4 inches and is too insensitive for detonation with ordinary pentaerythritol tetranitrate core fuse, which method comprises putting a mass of the composition in place for blasting, combining with the mass a sensitive water-resistant booster having a detonation pressure of at least 130,000 atmospheres and comprising at least 20 grams of weight and of a material selected from the group which consists of cast and pressed pentolite, pressed tetryl and pressed cyclotrimethylenetrinitramine, and detonating the combination booter and plastic mass with a conventional detonator.

3. The method of blasting with a liquid-plasticized high ammonium nitrate composition which contains aluminum and an explosive sensitizer and which has a density of at least about 0.8 gram per cubic centimeter and has in a long column a critical diameter of at least about 4 inches and is too insensitive for detonation with ordinary pentaerythritol tetranitrate core fuse, which comprises putting a mass of the composition in place for blasting, combining with the mass a sensitive water-resistant booster having a detonation pressure of at least 130,000 atmospheres and comprising at least 20 grams weight and of a material selected from the group which consists of cast and pressed pentolite, pressed tetryl and pressed cyclotrimethylenetrinitramine, and detonating the combination booter and plastic mass with a conventional detonator.

4. In combination, a water-containing slurried mass of high ammonium nitrate explosive, said mass containing a major proportion of said nitrate and also containing aluminum, said mass having a density of at least 0.8 gram per cubic centimeter, being insensitive to reliable detonation by ordinary standard pentaerythritol tetranitrate core fuse and having in a long column a critical di ameter of at least 4 inches, and a sensitive booster capable of producing a detonation pressure of at least 130 kilo atmospheres and composed primarily of Water. resi tant material selected from the group which consists of pressed and cast pentolite, pressed tetryl, and pressed cyclotrimethylenetrinitramine, said booster having a mass of at least 20 grams to assure reliable detonation of said high explosive.

5. In combination, a slurried water-containing mass of high ammonium nitrate explosive containing a major proportion of said nitrate, water, aluminum, and a self explosive sensitizer, said mass having a density of at least 0.8 gram per cubic centimeter, being insensitive to reliable detonation by ordinary standard pentaerythritol tetranitrate core fuse and having a critical diameter of at least 4 inches, and a sensitive booster capable of producing a detonation pressure of at least 130 kilo atmospheres and composed primarily of water resistant material selected from the group which consists of cast and pressed pentolite, pressed tetryl and pressed cyclotrimethylenetrinitramine, said booster having a mass of at least 20 grams to assure reliable detonation of said high explosive.

6. Combination according to claim 4 wherein the booster consists primarily of cast 50'-50 pentolite.

7. Combination according to claim 4 wherein the slur ried high explosive mass contains 15 to 20% of water to make a slurry and wherein the booster is at least equivalent in detonating power to 50-50 pentolite.

References Cited UNITED STATES PATENTS 10 2,754,755 7/1956 Ruth et a1. 10224 2,913,982 11/1959 Hayes 102-24 2,930,685 3/1960 Cook et a1. 149-15 3,032,450 5/1962 Blackwell 149-7 15 CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGE'IT, Examiner. L. A. SEBASTIAN, Assistant Examiner. 

1. IN COMBINATION, A MASS OF HIGH AMMONIUM NITRATE EXPLOSIVE CONTAINING A MAJOR PROPORTION OF SAID NITRATE AND A FUEL OIL, SAID MASS BEING INSENSITIVE TO RELIABLE DETONATION BY ORDINARY PENTAERYTHRITOL TETRANITRATE CORE FUSE, AND HAVING IN A LONG COLUMN A CRITICAL DIAMETER OF AT LEAST 4 INCHES, AND A SENSITIVE BOOSTER CAPABLE OF PRODUCING A DETONATION PRESSURE OF AT LEAST 130 KILO ATMOSPHERES AND COMPOSED PRIMARILY OF WATER RESISTANT MATERIAL SELECTED FROM THE GROUP WHICH CONSISTS OF PRESSED AND CAST PENTOLITE, PRESSED TETRYL AND PRESSED CYCLOTRIMETHYLENETRINITRAMINE, SAID BOOSTER HAVING A MASS OF AT LEAST 20 GRAMS TO ASSURE RELIABLE DETONATION OF SAID MASS OF HIGH EXPLOSIVE. 